Improve VirtualHostService#getBaseURL to use scheme from request

http://hippo.2275632.n2.nabble.com/doAction-PRG-and-HTTPS-td7579980.html

We need to add HstRequestUtils#getRequestScheme() that contains

request.getHeader("X-Forwarded-Scheme");
if the above is null (HTTP/1.0) fallback to request.getScheme()

and use this in VirtualHostService#getBaseURL to create the url

After this, PRG should use the scheme from forwarded request